I. Field of the Invention
The present invention relates to antenna technology. In particular, the invention relates to the integration of multiple antennas to allow communications over multiple frequency ranges.
II. Related Art
In recent years there has been significant growth in the availability and use of terrestrial cellular wireless services. At the same time, a new generation of satellite-based telephony systems is becoming available. As a result there is a growing need for wireless devices such as wireless telephone equipment capable of accessing services offered by both terrestrial cellular and satellite-based telecommunication systems. The antennas used by this equipment must, therefore, be capable of dual-mode, dual frequency operation.
A number of problems arise when attempting to meet this need with current antenna technologies. A single antenna aperture design covering both the cellular frequency range (approximately 824 to 960 MHz) and typical satellite communications bands (for example, 2484 to 2500 MHz) would require multioctave bandwidth operation. In addition, the aperture would require dual polarization capabilities since the preferred polarization is different for each mode. Vertical polarization is commonly used for cellular communications, and circular polarization typically used for satellite communications. Supporting both kinds of communications is extremely difficult with a single antenna assembly. Stacked microstrip patch antennas are a possibility, since they offer the potential for dual-band operation. When considering the implementation of such antennas in handheld wireless devices or phones, however, their sizes at cellular frequencies are prohibitive.
If separate wire-type antennas such as dipoles, monopoles, or helix antennas are used to service each frequency band, the electromagnetic coupling between the two antennas could cause severe distortion in the antennas"" respective radiation patterns, thereby reducing the effectiveness of each antenna. For handheld phones, this means that one antenna would have to be retracted while the other is deployed, to minimize the deleterious effects of electromagnetic coupling. For fixed and vehicular applications, separate antennas imply multiple installation sites with one antenna physically displaced far enough away from the other to minimize the interaction between them. Multiple antenna installations increase the size, cost, and complexity of the telephone installation.
Consequently, there is a need for an antenna assembly that permits communications over both cellular and satellite frequency ranges, and is physically compact, but does not suffer from electromagnetic coupling problems when operating in either range.
The present invention represents an integrated antenna assembly comprising a cellular communications antenna and a satellite communications antenna. Such an antenna assembly can therefore be used for communications over either frequency range. A wireless telephone using this assembly can, therefore, operate with either a terrestrial cellular communications system or a satellite communications system. In a preferred embodiment of the invention, the satellite communications antenna is a quadrifilar helix antenna and the cellular communications antenna is a sleeve dipole. The whip portion of the sleeve dipole is positioned axially in the center of the quadrifilar helix antenna. This orientation permits operation in both the satellite and cellular frequency ranges without significant electromagnetic coupling.
The invention has the feature of providing cellular and satellite frequency capability in a single antenna assembly.
The invention has the additional feature of providing electromagnetic interference protection to circuitry incorporated in the antenna assembly, such as signal filtering and low-noise amplification circuitry.
The invention has the advantage of providing dual frequency operation in such a manner that electromagnetic coupling between antennas is minimal.
The invention has the further advantage of providing dual frequency operation in an antenna assembly that is relatively compact.